The present invention relates to wheels for railway cars and more specifically to steel wheels having a structure to provide low axial flange deflection and low residual tensile stress from thermal cycling, which generally results from brake shoe friction heating on the wheel tread surface.
Railway wheels are provided in various shapes, which shapes were generally devised for specific applications or to overcome a specific problem, such as wheel deflection and residual stress. Steel railway wheels may be machined, formed, wrought or cast. Each of the following variations or configurations of materials, shape and structure were provided to compensate for, or to overcome, one of the above-noted problems. Illustrative of an early attempt to resolve a plurality of problems in a single structure is the wheel taught and illustrated in U.S. Pat. No. 2,768,020 to Sylvester, which provided a cast steel wheel to compensate for or to overcome the inherent residual stresses generally attributed to cast steel wheels, as compared to chilled iron or wrought steel wheels. The wheel structure had a contour and form intended to hinder the formation of residual stresses as-cast wheels. The structure taught and illustrated included a larger plate and fillet construction at both the hub and rim connections to the plate segment. In addition, it was noted that this disclosed cast steel wheel structure was to provide a wheel having an increased capacity to dissipate heat generated in the rim of the wheel as compared to earlier cast steel wheel arrangements. The Sylvester-'020 patent asserted a railway wheel form and contour with increased strength without increased material mass to accommodate higher wheel load capacity. This may be equatable to asserting a wheel with greater load carrying capacity without a concomitant increase in the overall mass of the wheel. In the illustrated structure of this Sylvester-'020 patent, the plate or web portion has a generally straight cross-sectional area and the fillets are contoured or angled to smoothly blend into the rim to provide maximum mass at the rimfillet engagement points. This cast steel wheel form and contour was to provide high operational resistance to thermal checking and cracking under severe loading and braking conditions. However, there was no appreciation or discussion of the disclosed wheel structure effect, if any, upon wheel deflection, that is a displacement of the wheel flange about the hub, with the increase in temperature associated with braking conditions. In the context of the present application, wheel deflection refers to movement of the wheel flange generally in a wheel inboard or outboard direction and parallel to the longitudinal axis of the wheel. As the rim is rigidly connected to the wheel hub by the web or plate, there is an axial component to the deflection. Wheel deflection will be further described below.
U.S. Pat. No. 3,038,755-Keysor recognized prior wheels are, to a greater or lesser extent, subject to stress cracks in the plate portion of the wheel in the areas adjacent to the hub and the rim. Further, he identified the fact that stress cracks in the plate portion of the wheel were initiated primarily by repeated braking applications, which developed large heat concentrations generated from frictional contact of brake shoes on the wheel rim. This elevated temperature condition in the wheel rim induced expansion in the radial direction, which expansion created highly concentrated stress patterns in the plate portion of the wheel. The high stress areas were likely to develop cracks from repeated expansion and contraction with repeated brake applications, which can potentially result in ultimate wheel failure. The railway wheel taught in the Keysor-'755 patent disclosure particularly provided a railway wheel for repeated servicing. The requirement of a wheel with increased fatigue life expectancy was also recognized and identified, which wheel would be inherently resistant to stress cracks from repeated brake applications during service. The disclosure specifically taught a wheel plate having an arcuate cross-sectional contour. The plate of the wheel is tangent to a line lying in a plane positioned midway between the front and rear surfaces of the hub and normal to the axis of rotation of the wheel, which point of tangency lies within the hub. Parabolic curves were particularly taught for the fillets, which are provided at the intersections between the hubs and the flange or rim portions of the wheel. The specific parabolic curves for each fillet vary with a particular size and style of cast wheel. The structure taught and illustrated in the Keysor-'755 patent provided a wheel with an arcuate plate connected to the hub and the rim by fillets having a gradually changing radius of curvature, which structure was asserted to substantially lessen the shock fatigue or the impact from shock fatigue and stress cracks, and improved the strength of these wheels as compared to prior art wheels. Along with this improved strength characteristic, this wheel structure was reported to decrease the weight of the wheel while providing the same rated or weighted service and life as earlier prior art wheels.
U.S. Pat. No. 4,145,079 to Greenfield et al. teaches a railroad car wheel structure, but recognized that there is a continuing problem between fracture in the regions of connections between the wheel plate and hub or rim, when the wheel is subjected to the stresses from usage on rail cars. Heat induced fracture or fissuring was recognized as being generated from contact between the brake shoe and wheel during normal braking operations. More particularly, the expansion-contraction of thermal cycling from braking induced residual stresses and fracturing. This patent acknowledged that previous efforts to minimize the effects of the mechanical and thermal stresses have included increasing the surface area for better heat dissipation, increasing the metal volume for added strength and modifying the configuration of the plate that connects the hub and the rim.
A particular kind of plate, noted as a B-28 and D-28, are straight plate wheels. Similarly two curved plate designs were noted as CB-28 and CD-28, which are indicated as being the same as B-28 and D-28 except for their rim thickness. Inboard and outboard concave curved surfaces or fillets at each connection define transition regions between the hub or the rim and the plate. These curved surfaces provide a smooth progression or transitional area from the plate to the hub or rim and are intended to minimize stress concentration in these areas. Similarly wrought steel straight plate wheels of the B-28 configuration have been known to have a tendency to crack in the rear or inboard rim-to-plate fillet and in the front or outboard hub-to-plate fillet. As a result, a D-28 wheel incorporated a design change with a greater cross-section in the area of the hubbed plate connection and the curved transitional surfaces were provided with parabolic curves having their major axis disposed generally in the radial direction from the web. The sole intention of many of these changes in wheel structures is to reduce the level of stress in the critical transition zones regions between the hub or rim and the plates.
The Greenfield-'079 patent considered the tangential, vertical and lateral mechanical loads as well as the thermal loads from braking. The wheel structure placed the rim, hub and plate in a specific configuration, which potentially minimizes the need for transitional fillets or radii. The plate is arranged to join the hub adjacent to its in-board edge and the in-board conical surface of the plate merges into the inner radial surface of the hub. The juncture between the rim and plate is arranged for at least one of the in-board and out-board conical surfaces of the plate to merge directly into the respective radial in-board or radial out-board surface of the rim. There are several embodiments illustrated in this application but the configurations provide for the cantilever arrangement of the rim to the plate allowing distortion during load application to the rim, as in braking. Physical movement within the wheel itself is considered to provide counteradditive, rather than additive, stresses to those stresses present due to vertical and lateral loading. This movement purportedly reduces the overall stress to provide substantial improvements over straight plate design and to achieve operating stresses within acceptable limits as their proposed inventive concept. However, it is the direct merger of at least one of the surfaces defined by the plate into at least one radial edge of each of the hub and rim that minimizes the usage of traditional concave transitional fillets, which is thought to provide improved resistance to the stress concentration in these critical areas.
U.S. Pat. No. 4,471,990-Hirakawa provides a railroad car wheel formed by rolling, which wheel has fillets formed so that each has an angle of inclination of approximately 20 degrees with respect to the horizontal direction. The connecting portions of the plate are perpendicular to the axis of the wheel and are preferably as long as possible. The wheel plate portion is connected to the bossed portion at a point displaced somewhat inwardly in the center of the width of the bossed portion with respect to the track, that is the hub portion and the plate portion are connected to the rim substantially in the middle of the width of the rim. This car wheel is provided with a shape to minimize internal residual stress after extraordinary brake force is applied to the wheel at its rim. There is no accommodation for wheel deflection associated with wheel operation nor is the discussion directed to the radial expansion of the wheel during normal operations.
U.S. Pat. No. 5,039,152-Esaulov et al. provides a railway wheel defined by a plurality of equations and basic wheel parameters including the diameter of the rolling surface and the outside diameter of the hub. The aim of this apparatus and its disclosure is to provide a railway wheel configuration to insure mutual compensation of stresses arising in the wheel under a complex load. In this disclosure, the "plate" joining the hub and the rim has a median longitudinal axis and curveilinear generating lines "conjugating" the configurations of the rim and hub by radius curves of a radius determined from a given mathematical equation or expression. The cross-sectional area of the disc, which is defined by a cylindrical secant surface coaxial with the hub, is equidimensional, but the "point of conjugation" of the median longitudinal axis of the disc with the hub is offset from its middle and the median longitudinal axis of disc configuration has rectilinear portions with curvilinear portions interposed therebetween. The rectilinear portion of the median longitudinal axis of the disc at the side of the rim conjugating with the first curvilinear portion is described by a second equation and this conjugates with the second curvilinear portion described by a further expression and each of the succeeding curvilinear portions are defined by equations. In summary, the structure of the wheel has a curvilinear portion that has a complex of at least three curved segments in the plate joining the hub and the rim and, both forward and reverse fillets apparently defined with the same radii joining the curvilinear disc or plate portion. This complex wheel structure is the product of specific analyses and structural arrangements defined by a plurality of equations. The disclosed structure provides variations in the shapes of a central joining plate to accommodate variations in stress between the tensile and tangential stresses at the rim due to thermal and mechanical loads.